|
Use
of admixtures for accelerating setting & hardening of cement has its own
limitations. Though High Alumina Cement can be used for getting early strength
properties but it exhibits retrogression of strength when exposed to hot &
humid conditions.
Regulated-set
cement incorporates set control and early-strength-development components.
The
Regulated-set cement consists essentially of a mixture of Portland Cement
containing calcium fluoro-aluminate (C11A7. CaF2)
with an appropriate retarder (usually citric acid). The early strength
development is controlled by the content of Calcium fluoro-aluminate.
With
5% of calcium fluoro-aluminate, about 6 MPa strength can be
achieved in 1hr; With 50% 20 MPa can be achieved in 1
hr.
The
setting time of cement varies between 1 and 30 minutes (generally 15 to
20 min) with corresponding rapid early strength development. Citric acid used
as a retarder can extend the setting time by as much as 1 hr. Obviously,
early strength is affected by retarder usage.
Compared
to conventional Portland cement, regulated-set cement contains a reduced
proportion of dicalcium silicate and no tricalcium aluminate. It does
contain a new ternary compound called calcium
fluoroaluminate to produce very high early strengths and short set times.
These cements allow less handling time &
release lot of heat. Their sulphate resistance is poor.
Can be used for very high early (3-4hr) strength
concrete & mortar, emergency/patch repairs, construction between tides,
quick release of forms in precast concrete products industry.
Regulated-Set
Cement is known as Schnellzement in Japan,
Austria
& Germany.
|
